What does the patent invalidation defense mean?

After an application for a patent is authorized, it is called an invalid patent because it exceeds the statutory protection period, or because the patentee fails to pay the annual patent fee in time, or any individual or unit requests to declare the patent invalid, and it is determined by the Patent Reexamination Board and declared invalid. Invalid patents are no longer binding on the use of the technology involved. Any unit or individual can use it for free, thus obtaining economic benefits. As a kind of industrial property right, patent right is the exclusive right granted to inventors and designers by the Patent Office. Patent right is a kind of property right, which is exclusive. Without the permission of the patentee, no unit or individual may exploit its patent. The invalid patent loses this right, that is, it loses the protection of the patent law, and any unit or individual can use it free of charge. Any unit or individual can improve invalid patents and implement them free of charge. For example, suppose there is no cup for water. A invented the cup, B improved the cup A and added the handle. The cup with handle will improve the function of the cup: it is convenient to take water; A cup filled with hot water is not afraid of scalding. However, it is impossible for the handle to exist independently from the cup, otherwise the function of the handle will be lost. That is to say, B has improved A's invention and made a new invention, and it is impossible to be separated from A's invention. If A's invention becomes an invalid patent, there is no need to pay A patent technology use fee after B's improvement is implemented.